Effect of ozone on net photosynthesis in oat (Avena sativa) and duckweed (Lemna gibba)

Short exposure to ozone depressed photosynthesis in both oat and duckweed at concentrations above 140 microg m(-3) and 300 microg m(-3), respectively. The effect on exposed oat flag leaves was age-dependent, with maximum susceptibility to ozone 10-20 days after emergence of the panicle. In duckweed, photosynthesis was more sensitive to differences in ozone concentration than to differences in duration of exposure.     

The use of terrestrial plant biomass as a parameter in the fugacity model

A new compartment, the terrestrial plant biomass, is proposed for inclusion in the fugacity model. Two possibilities of calculation have been developed and exemplified: the first considers the plant as a whole, the second takes into account foliage, trunk and roots separately.     

Biliary secretion,retention and excretion of five 14C-labelled polychlorinated biphenyls in the rat

Five ¹⁴C-labelled polychlorinated biphenyls: 2,4′,5-trichlorobiphenyl, 2,2′,4,5′-tetrachlorobiphenyl, 2,2′,4,5,5′-pentachlorobiphenyl, 2,2′,3,4,4′-pentachlorobiphenyl and 2,2′,4,4′,5,5′-hexachlorobiphenyl were administered orally to bile-cannulated rats. The activity secreted in the bile, excreted in the feces and the urine was determined. Residues of radioactivity in certain tissues and the carcass were also measured.The trichlorobiphenyl showed the highest absorption (93.8%±5.4) from the gastrointestinal tract and biliary secretion of radioactivity (87.6%±6.1 of the dose). The hexachlorobiphenyl showed the lowest absorption and biliary secretion, 28.2%±1.4 and 18.6%±1.3, respectively. The urinary excretion was low and the radioactive residues in the eviscerated carcasses increased with the chlorine content of the biphenyls.     

Induction of aryl hydrocarbon hydroxylase by chlorinated dibenzofurans in rats

Five of 25 chlorinated dibenzofurans induced aryl hydrocarbon hydroxylase in rats when administered orally at 40 μg/kg body weight. Active inducers included the three congeners with chlorines in all four lateral positions and the 2,7- and 2,8-dichlorodibenzofurans. The findings agree well with other studies involving common congeners, but do not agree with findings in that congeners with three lateral chlorines were inactive .     

Transformation and adsorption of Fenamiphos, f. sulfoxide and f. sulfone in molokai soil and simulated movement with irrigation

The ban of commonly used soil fumigants, DBCP and EDB, for control of nematodes in pineapple fields has prompted investigations into a non-fumigant nematicide, fenamiphos (Nemacur^®). The transformation and adsorption in soil of fenamiphos and its transformation products, f. sulfoxide and f. sulfone were studied in the laboratory. Fenamiphos adsorption on soil exceeded that of f. sulfoxide and f. sulfone. F. sulfoxide, however, was the most persistent. A one-dimensional simulation model was used to assess the impact of transformation and adsorption on the mobility and distribution of fenamiphos and f. sulfoxide in soil. Simulated results showed that fenamiphos stayed in the topsoil and transformed rapidly to f. sulfoxide. Because of the persistence and mobility of f. sulfoxide, this metabolite leached rapidly and significant amounts remained in the soil. This suggests that for times exceeding three weeks, f. sulfoxide may be the dominant compound providing nematode control in drip-irrigated pineapple.     

Effects of elevated CO2 concentration on the polyamine levels of field-grown soybean at three O3 regimes

Effects of increased ozone (O3) and carbon dioxide (CO2) on polyamine levels were determined in soybean (Glycine max L. Merr. cv. Clark) grown in open-top field chambers. The chamber treatments consisted of three O3 regimes equal to charcoal filtered (CF), non-filtered (NF), and non-filtered plus 40 nl litre(-1) O3 and CO2 treatments equal to 350, 400 and 500 microl litre(-1) for a total of nine treatments. Leaf samples were taken at three different times during the growing season. Examination of growth and physiological characteristics, such as photosynthesis, stomatal resistance, and shoot weight, revealed that increasing CO2 ameliorated the deleterious effects of increased O3. Results from the initial harvest, at the pre-flowering growth stage (23 days of treatment), showed that increasing O3 at ambient CO2 caused increases in putrescine (Put) and spermidine (Spd) of up to six-fold. These effects were lessened with increased CO2. Elevated CO2 increased polyamines in plants treated with CF air, but had no effect in the presence of ambient or enhanced O3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O3-induced increases in Put and Spd at ambient CO2 concentrations. However, increased CO2 levels inhibited this response by blocking the O3-induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O3 or CO2 effects on polyamine levels. Our results demonstrate that current ambient O3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO2 to protect soybeans from O3 damage, however, does not appear to involve polyamine accumulation.